1. Field of the Invention
This invention relates to semiconductor device packages, and more specifically to semiconductor device packages which are shielded to protect against electromagnetic interference (EMI).
2. Description of the Related Art
Semiconductor device packages typically have electrical circuitry implemented on a circuit substrate, such as a printed circuit board or a ceramic substrate. The performance of the circuitry may be adversely affected by electromagnetic interference (EMI). Electromagnetic interference (EMI) is the generation of undesired electrical signals, or noise, in electronic system circuitry due to the unintentional coupling of impinging electromagnetic field energy.
The coupling of signal energy from an active signal net onto another signal net is referred to as crosstalk. Crosstalk is within-system EMI, as opposed to EMI from a distant source. Crosstalk is proportional to the length of the net parallelism and the characteristic impedance level, and inversely proportional to the spacing between signal nets.
Electronic systems are becoming smaller, and the density of electrical components in these systems is increasing. As a result, the dimensions of the average circuit element is decreasing, favoring the radiation of higher and higher frequency signals. At the same time, the operating frequency of these electrical systems is increasing, further favoring the incidence of high frequency EMI. EMI can come from electrical systems distant from a sensitive receiving circuit, or the source of the noise can come from a circuit within the same system (crosstalk or near source radiated emission coupling). The additive effect of all these sources of noise is to degrade the performance, or to induce errors in sensitive systems.